This invention relates to apparatus for mounting and dismounting a submerged propeller unit to and from the hull of a floating body from the outside thereof. More particularly, it relates to new and improved apparatus of this character which is of particular utility in connection with turnable steering propellers mounted on vertical driving shafts, so-called thrusters, which are used with deeply submerged floating bodies of the type that support oil drilling rigs.
Apparatus has been proposed heretofore for mounting and dismounting a propeller unit with a vertical drive shaft at the bottom of a vessel without docking the vessel. In one such arrangement (disclosed in Swedish Pat. No. 181,061), the work of mounting or dismounting the propeller unit takes place in a chamber or barrel in the vessel which has an open upper end located above the waterline of the vessel and a lower end secured in watertight relation to the bottom an opening therein. In practice, the propeller unit is lowered into position through the barrel and fastened by flanges forming a closure for the opening in the vessel bottom. Alternatively, the propeller unit may be raised into position from the outside of the vessel and thereafter secured to the hull by bolts inserted from inside the barrel.
Outside mounting has many advantages, especially for large vessels, since it eliminates the necessity for transporting the propeller unit within the vessel. The open barrel technique requires so much space, however, that it is not practical. In some cases, it is possible to pressurize the space in which the mounting or dismounting work is to be done so as to keep the water out of it. Working in a pressurized space, however, introduces further difficulties that make this technique unattractive.